M. Meyyappan Director, Center for Nanotechnology NASA Ames Research Center Moffett Field, CA 94035 meyya@orbit.arc.nasa.gov web: http://www.ipt.arc.nasa.gov
• Nanoelectronics (CNTs, molecular electronics) • Non-CMOS circuits and architectures, reconfigurable systems • Spintronics, quantum computing, nanomagnetics • Nanophotonics, nano-optics, nanoscale lasers…. • Chemical and biological sensors • Novel materials for all applications (CNTs, quantum dots, inorganic nanowires… • Integration of nano-micro-macro • Bio-nano fusion • • •
• Carbon Nanotubes - CNT - growth and characterization - CNT based nanoelectronics - CNT based microscopy - CNT interconnects - CNT based biosensors - CNT chemical sensors • Some other Nano examples - Inorganic nanowires - Protein nanotubes - Nano in gene sequencing
CNT is a tubular form of carbon with diameter as small as 1 nm. Length: few nm to microns. CNT is configurationally equivalent to a two dimensional graphene sheet rolled into a tube. CNT exhibits extraordinary mechanical properties: Young’s modulus over 1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa. CNT can be metallic or semiconducting, depending on chirality.
• The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture • Young’s modulus of over 1 TPa vs 70 GPa for Aluminum, 700 GPA for C-fiber - strength to weight ratio 500 time > for Al; similar improvements over steel and titanium; one order of magnitude improvement over graphite/epoxy • Maximum strain ~10% much higher than any material • Thermal conductivity ~ 3000 W/mK in the axial direction with small values in the radial direction
• Electrical conductivity six orders of magnitude higher than copper • Can be metallic or semiconducting depending on chirality - ‘tunable’ bandgap - electronic properties can be tailored through application of external magnetic field, application of mechanical deformation… • Very high current carrying capacity • Excellent field emitter; high aspect ratio and small tip radius of curvature are ideal for field emission • Can be functionalized
• CNT quantum wire interconnects • Diodes and transistors for computing • Capacitors • Data Storage • Field emitters for instrumentation • Flat panel displays • THz oscillators Challenges • Control of diameter, chirality • Doping, contacts • Novel architectures (not CMOS based!) • Development of inexpensive manufacturing processes
• High strength composites • Cables, tethers, beams • Multifunctional materials • Functionalize and use as polymer back bone - plastics with enhanced properties like “blow molded steel” • Heat exchangers, radiators, thermal barriers, cryotanks • Radiation shielding • Filter membranes, supports • Body armor, space suits Challenges - Control of properties, characterization - Dispersion of CNT homogeneously in host materials - Large scale production - Application development
Challenges • CNT based microscopy: AFM, STM… • Nanotube sensors: force, pressure, chemical… • Controlled growth • Functionalization with • Biosensors probe molecules, robustness • Molecular gears, motors, actuators • Integration, signal processing • Fabrication techniques • Batteries, Fuel Cells: H 2 , Li storage • Nanoscale reactors, ion channels • Biomedical - in vivo real time crew health monitoring - Lab on a chip - Drug delivery - DNA sequencing - Artificial muscles, bone replacement, bionic eye, ear...
• CNT has been grown by laser ablation (pioneering at Rice) and carbon arc process (NEC, Japan) - early 90s. - SWNT, high purity, purification methods • CVD is ideal for patterned growth (electronics, sensor applications) - Well known technique from microelectronics - Hydrocarbon feedstock - Growth needs catalyst (transition metal) - Multiwall tubes at 500-800° deg. C. - Numerous parameters influence CNT growth
- Surface masked by a 400 mesh TEM grid - Methane, 900° C, 10 nm Al/1.0 nm Fe/0.2 nm Mo
- Surface masked by a 400 mesh TEM grid; 20 nm Al/ 10 nm Fe; nanotubes grown for 10 minutes Grown using ethylene at 750 o C
• Inductively coupled plasmas are the simplest type of plasmas; very efficient in sustaining the plasma; reactor easy to build and simple to operate • Quartz chamber 10 cm in diameter with a window for sample introduction • Inductive coil on the upper electrode • 13.56 MHz independent capacitive power on the bottom electrode • Heating stage for the bottom electrode • Operating conditions CH 4 /H 2 : 5 - 20% Total flow : 100 sccm Pressure : 1 - 20 Torr Inductive power : 100-200 W Bottom electrode power : 0 - 100 W
*First single nanotube logic device – Inverter demonstration (Appl. Phys. Lett., Nov. 2001) by Chongwu Zhou (USC) and Jie Han (NASA Ames) V ou t n-type p-type 100 V 0 V DD DS (nA) Carbon nanotube V DS =10 mV 80 p-MOSFET 60 V in I 40 20 0 2.5 -20 -15 -10 -5 0 V DD = 2.9 V V g (V) 2.0 V DD V out (V) 1.5 p DS (nA) 12 V DS =10 mV V i V ou n-MOSFET 1.0 n 8 n t 0 0.5 4 V 0.0 0 0.0 0.5 1.0 1.5 2.0 2.5 -10 -5 0 5 10 V g (V) V in (V)
As device feature size continues to shrink (180 nm 130 nm 100 nm) and chip density continues to increase, heat dissipation from the chip is becoming a huge challenge.
(Beyond the SIA Roadmap for Silicon) • Must be easier and cheaper to manufacture than CMOS • Need high current drive; should be able to drive capacitances of interconnects of any length High level of integration (>10 10 transistors/circuit) • High reproducibility (better than ± 5%) • • Reliability (operating time > 10 years) • Very low cost ( < 1 µcent/transistor) • Better heat dissipation characteristics and amenable solutions • Everything about the new technology must be compelling and simultaneously further CMOS scaling must become difficult and not cost-effective. Until these two happen together, the enormous infrastructure built around silicon will keep the silicon engine humming….
• Neural tree with 14 symmetric Y-junctions • Branching and switching of signals at each junction similar to what happens in biological neural network • Neural tree can be trained to perform complex switching and computing functions • Not restricted to only electronic signals; possible to use acoustic, chemical or thermal signals
Atomic Force Microscopy is a powerful technique for imaging, nanomanipulation, as platform for sensor work, nanolithography... Conventional silicon or tungsten tips wear out quickly. CNT tip is robust, offers amazing resolution. Simulated Mars dust 2 nm thick Au on Mica
DUV Photoresist Patterns Generated by Interferometric Lithography Nguyen et al., App. Phys. Lett., 81, 5, p. 901 (2002).
Red Dune Sand (Mars Analog) Optical image AFM image using carbon nanotube tip
DNA PROTEIN
MWNT Interconnects ? CNT advantages: (1) Small diameter (2) High aspect ratio (3) Highly conductive along the axis (4) High mechanical strength Question: How to do this ?
Bottom-up Approach for CNT Interconnects Metal Deposition Ti, Mo, Cr, Pt SiO 2 /Si Catalyst Top Metal Layer Patterning Deposition Ni Plasma At ~ 400 to CVD CMP 800° C TEOS CVD J. Li, Q. Ye, A. Cassell, H. T. Ng, R. Stevens, J. Han, M. Meyyappan, Appl. Phys. Lett ., 82 (15), 2491 (2003)
• Our interest is to develop sensors for astrobiology to study origins of life. CNT, though inert, can be functionalized at the tip with a probe molecule. Current study uses AFM as an experimental platform. • The technology is also being used in collaboration with NCI to develop sensors for cancer diagnostics - Identified probe molecule that will serve as signature of leukemia cells, to be attached to CNT - Current flow due to hybridization will be through CNT electrode to an IC chip. - Prototype biosensors catheter development • High specificity • Direct, fast response • High sensitivity • Single molecule and cell signal capture and detection
The Fabrication of CNT Nanoelectrode Array (1) Growth of Vertically Aligned CNT Array (2) Dielectric Encapsulation (3) Planarization (4) Electrical Property Characterization By Current-sensing AFM re ce (5) Electrochemical Potentiosta t Characterization we
Fabrication of CNT Nanoelectrodes J. Li et al, Appl. Top view 45 degree perspective view Phys. Lett ., 81 (5), 910 (2002) Side view after encapsulation Top view after planarization
Electrical Properties of CNTs 10 +1mA 5 Current (nA) 0 0 -5 -10 -1mA -5.0 -2.5 0.0 2.5 5.0 -5V 0 +5V Voltage Bias (mV) HP analyzer Current Sensing AFM Four-probe station And HP parameter analyzer
Chemical Functionalization i-Pr 2 NEt - CO 2 CO 2 H DMF Cy N C N Cy O HO N O H 2 N O Fc O O O N HN Fc O Fc = Fe Highly selective reaction of primary amine w ith surface –COOH group
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